The present invention pertains to internal combustion engine health monitoring, and particularly to engine diagnostics. More particularly, the invention pertains to detection of engine ignition misfiring.
Engine misfiring reduces the power output of the engine, and causes poor performance, engine roughness, low fuel economy, deterioration of the catalytic converter, and increased pollution. Catalytic converters will have reduced life expectancy and efficiency because of unburned fuel passing to and combusting in the hot converter. Lack of converter efficiency results in more emissions. Incomplete burning of fossil fuels is a prime source of air pollution. An engine that misfires only two percent of the time, for example, may produce pollutant levels that exceed emission standards by 150 percent.
Present and proposed regulations in certain states require that vehicles have onboard devices for detecting and warning of engine misfire. Such devices must be capable of identifying which particular cylinder is misfiring, or in the case of multiple cylinder misfires, indicating that more than one cylinder is misfiring. A preference is for a system that can additionally determine which cylinders are misfiring in the case of multiple misfires, identify sporadic non-periodic misfiring events, and detect isolated misfires. Further, a system should be able to detect five or fewer misfires for every 1,000 firings, count the misfires and firings, and function at all normal engine speeds and any operating conditions.
Related-art engine misfire detection systems for misfire detection have used various approaches. Some examples are the detection of rotations-per-minute (RPM) fluctuations of engine output, absence of a spark or proper sparkplug current in the ignition system, exhaust pipe temperature changes, relative temperature differences among the exhaust ports, rotational torque variation, exhaust pressure pulsing and abnormal content of exhaust gases. None of these systems provide highly accurate and real-time determination of information required for the above-noted preferred misfire detection data. Piezo or pressure sensor-based systems suffer from structural noise, and thermocouple-based systems have short lifetimes. The present device has little or no structural noise and has a long lifetime. This device also can provide data accurately, reliably and at low cost.
The present invention is a misfire detector that senses firings and misfires of an internal combustion engine. The exhaust pipe coupled to the exhaust manifold has a window fabricated on a side so that an infrared (IR) light sensor proximate to the window can detect IR light emerging from the hot exhaust gases passing through the pipe. The window instead may be placed in the exhaust manifold or in a short separate piece of exhaust pipe, which may be inserted in-line as a part of the engine""s exhaust pipe. The window should be situated so that the exhaust gases are detected before they reach the catalytic converter. The temperature and position of the window is such as not to become opaque by solid deposits.
The window is made from a material that transmits IR light and is resistant to heat. Also, a narrow-band filter (e.g., an interference filter) may be placed proximate to the window or sensor. The filter may be an integral part of the window, if the filter is thermally robust and insensitive to temperature. The window is placed on or within a hole in or a cut out area of the exhaust pipe and is sealed about its border to prevent exhaust gases from escaping from around the window.
The sensor is placed proximate to the window sufficient to detect the IR light (i.e., thermal emission) from the gases. Exhaust gases may contain compounds such as CO2, H2O, CO, N2, O2, HC, NO, NO2 and so on. The IR light amounts to pulse-like signals corresponding to the ignited air-fuel mixtures emanating from the cylinders. Examples of a fuel are gasoline, ethanol, kerosene, mixtures of various fuels, and so forth. If there is a misfire, then there will be a corresponding change in the pulse-like IR signal since the unburned gases will be different in temperature, composition or pressure from the bursts of burned gases emanating from the cylinders. The exhaust gas both emits and absorbs light in a manner dependent on composition, temperature, pressure and wavelength; and the net amplitude of the light wavelengths emerging from the gas is thus indicative of the nature of the exhaust gas.
The sensor converts the sensed IR light signal into electrical signals representing the IR signals, which in turn indicate the nature of the exhaust gas, which in turn indicates the proper operation of a cylinder. The electrical signals are fed into an onboard processor, which may be the engine processor. These signals are correlated or synchronized with ignition signals going to the spark plugs of a four-cycle or two-cycle engine. This correlation or synchronization with the ignition signals can be compensated for variation of the timing of the spark (such as the advance of the spark at higher engine RPM) relative to the cycle or stroke of the piston in the cylinder.
In the case of an engine not having an ignition system, such as some diesel engines, sensor output signals may be correlated or synchronized with a crankshaft position locator. The position locator may be a magnetic sensor situated on the crankshaft torsion-damper pulley or the like, which is on the end of the crankshaft. The pulley may have a piece of steel or iron adhered to its outer circumference that is sensed by the magnetic sensor.
Alternatively, a camshaft position indicator may be used to note the position of the crankshaft for a cam that has a fixed positional relationship relative to the crankshaft during operation of the engine. For cases wherein the camshaft position is varied relative to the crankshaft during operation of the engine, the processor may compensate for that effect. Also, there is a variable delay between the igniting of the gases and their passing by the window to be detected, which can be compensated for by the processor if it is desired to know which cylinder the detected hot gas pulse or cold gas comes from.
The processor may count in real-time the misfires and the firings over any set period of time. The processor can provide the number of misfires for each cylinder. Further, the processor may calculate the percentage of misfires relative to the total number of times that the engine should have firings during a given period of time, for certain cylinders or for all of the cylinders. If there is only one misfire, the processor can identify the specific cylinder having the misfire since the misfire is in the sequence of the total of the firings for the respective cylinders of the engine over a set period of time. The processor""s counter and memory can count and record all the firings or misfires of the engine. This information is available from the processor at any engine speed and under all operating conditions (e.g., cold operation, acceleration, hot operation, high-output power, low and high RPM, and normal operation).